Bicycles are more popular than ever as both a means of exercise and with seemingly ever increasing gas prices, as an energy efficient means of transportation. One of the biggest problems with bicycle transportation is the bicycle's limited cargo carrying capability.
A bicycle trailer is sometimes used to augment the cargo carrying capacity of a bicycle. Bicycle trailer designs exist for both carrying inanimate cargo as well as children. One example of a bicycle trailer that is designed to carry a child and even permit the child to partake in the propulsion of the bicycle/trailer combination is described in U.S. Pat. No. 7,845,664 which is incorporated herein in its entirety by reference.
Typically, a trailer is attached to an associated bicycle at its seatpost by a hitch assembly that permits the trailer being towed therebehind the ability to move/pivot vertically and laterally relative to the bicycle while in use. Most trailer hitch assemblies comprise three major components: (i) a bicycle attachment section; (ii) a trailer attachment section, which may be permanently secured to a frame section of the trailer; and (iii) a means for coupling the bicycle and trailer sections together, such as a quick release axle.
In most prior art designs the bicycle attachment section comprises a cylindrical and tubular portion that is received over the shaft of the seatpost. Often the fit between the tubular portion and the seatpost shaft permits the bicycle attachment section to pivot relative to the shaft's longitudinal axis thereby permitting the associated trailer to move laterally relative to the bicycle during use. The bicycle attachment section also includes a horizontally orientated bore through which a shaft or bolt of the coupling means can be received.
The trailer attachment section is often fixedly coupled to a frame of the trailer through welding, adhesive bonding, rivets and/or threaded fasteners to provide a secure link therewith. A front portion of the trailer attachment section is configured to interface with the portion of the bicycle attachment section having the horizontally orientated bore. The front portion also includes a horizontally orientated bore that is configured to align with the bore of the bicycle attachment section and receiving the coupling means therethrough. In many prior art hitch designs, one of the front portion of the trailer attachment section or a portion on the bicycle attachment section comprises a clevis and the other of the two comprises a protrusion that is received within the clevis.
As indicated above, the coupling means typically comprises a bolt that is received through the aligned bores and acts to transfer load between the bicycle and trailer attachment sections. The sections are also configured to pivot about the longitudinal axis of the bolt giving the associated trailer vertical compliance relative to the bicycle. In some hitches the bolt comprises a threaded fastener that is utilized in combination with a corresponding threaded nut. In other circumstances, the shaft is part of a quick release mechanism as is often used to secure the wheels of a bicycle to its frame and fork. Advantageously, the use of a quick release mechanism enables a user to easily detach the trailer attachment section from the bicycle attachment section without the use of tools to more easily facilitate use of the bicycle without the trailer.
A quick release mechanism used to secure a wheel to a bicycle is subject to very little dynamic loading and only a moderate to small amount of static loading. Rather, the loads experienced by a wheel during use are transferred to the frame of the bicycle by way of the wheels axle through which the quick release bolt passes. A relatively small tensile load is applied to the quick release mechanism's shaft when the quick release lever is closed and the associated nuts are compressed against the dropouts of the respective fork or frame to secure the wheel in place. In contrast, all load transferred through the bicycle to the trailer is transferred through the shaft of the quick release mechanism. These loads can become significant especially when one of the bicycle and the trailer twists relative to a longitudinal axis of the combined bicycle and trailer and the bolt resists the twisting by bracing up against the wall of the respective bores.
As can be appreciated, the failure of the bolt could have serious consequences freeing the trailer from the bicycle at an inopportune time. The passenger in the trailer could be injured even seriously. Further, a runaway trailer could hit people or objects causing injury and damage thereto.